they say the straight right is the best thing against a southpaw. so doesn't the same apply if you are a lefty? i always switched and could land the left or right from either side. that theory is overated. you have to commit to counters. all the slip or move this way etc means nothing if you do not impose your will to counter. there is no best way. a fighter who throws looping punches may not be able to counter with straight punches. every fighter is different. you can be taught how to counter but for some it is a gift.